High-performance electromagnetic transducer



July 31, 1962 o. N. BECKER 3, 4

HIGH-PERFORMANCE ELECTROMAGNETIC TRANSDUCER Filed Dec. 24, 1958 2SheetsSheet l FORCE INVENTOR. ADJUSTABLE CURRENT 5 ORLIEN N. BECKERSOURCE 1?. BY

ATTORNEY July 31, 1962 o. N. BECKER 3,047,777

' HIGH-PERFORMANCE ELECTROMAGNETIC TRANSDUCER Filed Dec. 24, 1958 2Sheets-Sheet 2 INVENTOR.

ORLIEN N. BECKER ATTOR E) United States Patent 3,047,777HIGH-PERFORMANCE ELECTROMAGNETIC TRANSDUCER Orlien N. Becker, AlderwoodManor, Wash, assignor to Minneapolis-Honeywell Regulator Company,Minneapolis, Minn, a corporation of Delaware Filed Dec. 24, 1958, Ser.No. 782,781 8 Claims. (Cl. 317-123) The present invention is directed toa high-performance type electromagnetic transducer and more particularlyto an improved linear moving iron armature type actuator. Devices ofthis type are generally old and the particular features of the presentinvention are directed to a double solenoid type actuator having animproved shape and arrangement of parts which provide a moving elementhaving a minimum of inertia for accurate high-speed actuation. Theparticular servo or transducer of the double solenoid type provides ahigh performance linear output. These objects and others will become apart of the reading of the attached description together with a drawingwherein: FIGURE 1 is :a schematic view of a moving iron segment in anair gap provided between a pair of poles shown for explanation purposes,FIGURE 2 is a similar schematic of a moving iron segment between twosets of poles, with a magnetic structure, also shown for explanationpurposes, FIGURE 3 is a sectional View of the actuator disclosing thearrangement, shape of parts and FIG- URE 4 is a top view or theactuator, and FIGURE 5 is a schematic wiring diagram for the actuator.

Referring to FIGURES 1 and 2, are included herein tor explanationpurposes for the operation and theory of the transducer it will be seenthat represents a segment or movable element of thin magnetic or ironmaterial suspended in an (air gap 11 defined Ibetween poles 1'2 and 13.The segment presents a very short path length to the magnetic fluxcombined with a large cross sectional area. As will he later seen, thisbasically be the relationship to parts here in my improved device. Inanalyzing this arrangement of parts, a set of physical units, inparticular a rationalized M.K.-S. system, in which all electrical unitsare practical and which incorporates the factor 41r into thepermeability of free space, are assumed. In FIGURE 1, the force F on theiron segment may be given by:

ang;

wherein as indicated on the sketch w is the width of the iron segmentand the width of the pole, x is the length of the segment positioned inthe gap, d is the total depth length and t is the thickness of the ironsegment. The permeance for the other part of the gap which does notinclude the segment will be expressed as:

ews -x Pb- 3) wherein Z is the length of the pole faceand l-x is theportion of the gap in which this segment is not positioned. The totalgap permeance is the sum oi. 1? and P or If the magnetomotive force 1 isproduced by an energizing winding, then IL wt 2 F- )nt (7) wherein n isthe number of turns in the winding and 1' is the excitation current. Itwill be apparent that this configuration is non-linear, since the outputforce varies as i In FIGURE 2, the moving iron segment or the actuatoris shown as moving between two sets of poles similar to the arrangementin FIGURE 1 to provide an output torce proportional to driving current,thus in FIGURE 2, the numerals 12 and 13 represent one set of poles andthe numerals 22 and 23 represent the second set of poles between each ofwhich is defined an air gap in which is positioned a portion of the ironsegment indicated generally at 25. Although not shown, it will beassumed that for purposes here that the iron segment 25 has the samedimension along the width of the poles and perpendicular to the plane ofthe paper :as does the pole width and that the segment number 25 ispositioned and movable in the gap between the poles and toward and awayiirom respective sets of poles 12 and 13 and 2 2, 23- maintaining thesame central locationship therein. Thus as in FIG- URE 2, if adifferential magnetornotive force f is superimposed on a referencemagnetomotive torce F in such a way as to add to the referencemagnetornotive iforce across one gap and subtract across the other gap,a net force is produced which tends to pull the segment into thestronger gap. The force tending to pull toward the gap indicated by 3.0in FIGURE 2 is +f1) Q52 T (a and the force tending to pull the segmenttoward the gap indicated at 31 in FIGURE 1 is 1 2 on 1 2 dx The netforce toward gap 30 is This is true since the segment moves out of thegap 31 at the same rate at which it enters the gap 30. Thus Thus-if F ismaintained constant, the net force exerted on 3 the segment isproportional to the differential magnetomotive force f and hence to thecurrent i in a differential winding or windings energizing the same.

Referring now to FIGURES 3 and 4, the improved electromagnetictransducer or moving iron type actuator Otf a subject invention is shownin FIGURE 3, in section, as including an annular magnetic outer shell ormagnetic yoke indicated at 40 to which is attached an end plate orclosure member 41 having a centrally located pole member 42 integraltherewith and extending toward the open extremity of the magnetic yoke.Although these parts may be integral, they are shown here as separateand held together by suitable means such as scr'ews indicated at 43.Positioned near the open extremity in the yoke is a first poleprojection or annularly raised rim 45 which extends inwardly toward saidpole member and forms therewith an air gap. A second pole memberindicated at 46 is also positioned near the open extremity of themagnetic yoke 40 and is spaced from the first polar projection or polering defining a second annular pole. While this pole ring may beintegral with the magnetic yoke, it is shown herein as a separate partsecured thereto through screw means such as is indicated in 44.Positioned within the yoke is a first winding 50 which is the mainbiasing or reference winding supplying the magnetomotive force or fluxto both of the poles :for purposes as will be later noted. Positionedadjacent thereto and within the confines of the yoke encircling the polemember 42 is a second coil 53 which as will be later noted supplies amagnetomotive force encircling both poles through a flux path whichextends from the pole member 42 through the poles 45, 46 the main bodyof the yoke 40 and back through the end plate 41 to the pole member 42.A third winding indicated at 55 is positioned between the polarprojections 45, 46 and as will be later noted supplies themagnetornotive force or flux which links only the pole member or polarprojection 46 through a path including the annular shell or yoke 40, theend plate 41 and the pole member 42 and across the air gap to the polarprojection 46. In the wiring diagram of FIGURE 5, the main winding isshown as connected to and energized from a continuous source of powerwhich will provide a magnetomotive force or flux through the corestructure linking both poles. FIG- URE also shows the 53 and 55 seriallyconnected and to an adjustable source or signal source which isvariable. The flux from the winding 53 links both of the pole memberswhile the flux from the coil 55 links only the polar projection or pole46 to provide the energization, coaction and operation outlined below.

Positioned in the air gaps between the polar members or projections 45,46 and the central pole member 42 is an annular segment of iron ormagnetic material indicated at 56 which is mounted on a supportingcup-shaped nonmagnetic member 51 to which an actuating shaifit 5'2 isadapted'to be connected. lSegment 56 is split as at 58 so that it willact as a segment and not a shorted turn in the magnetic fields. Theshaft and the supporting structure are adapted to be connected to thedevice to be operated and the shaft will be lightly journalled andpositioned so that it will maintain the position of the annular segment56 in the air gap concentricwith thepole member 42. Thus, as in FIGURE2, the segment is suspended between a pair of poles and has an effectivelength sub stantially equal to the distance between the center lines ofthe two polar projections 45 and 46 and is movable relative to the polarprojections concentric with the pole member 42. This high speedcylindrical solenoid type actuator, for purposes of explanation, has thefollowing turned ratio relationship between windings: winding 50 has Nturns, winding 53 has 11 turns and winding 55 has 2n turns. Thiscylindrical magnetic yoke arrangement is somewhat similar to a dynamicloudspeaker with the exception that a pair of poles are includedtherein. The winding 50 provides the reference magnetomotive force Fwhich appears between the central pole member and both poles 45, 46. Thewinding 53 provides a magnetomotive force or which as previouslyindicated also links both pole members 45, 46 and is connected in seriesfor energization purpose with the coil 53 which links only the pole 46.When all of the windings are energized, the magnetomotive torcedeveloped between the pole 45 and the central core member 42 is F-ni(where i is the current in windings 53, and the magnetomotiye torcedeveloped between the pole 46 and the central core member 42 can beexpressed as Fni+2ni which resolves or equals F+ni. This system istherefore linear, and since the width of the segment in the gap, and thewidth oi the poles may be expressed as W=1rr, wherein r is the radius ofthe air gap, the force output according to Equation 14 may be given asIt should be noted that operation is linear with the assumptionspreviously mentioned over the range where ni is smaller than F, sincethe force on the iron segment depends only upon the magnitude of the gapM.M.Fs. In this device, however, a further limitation must be imposedsince the flux density produced by the coil 50 or F and ni actingtogether must not be sufficient to saturate the magnetic yoke. Maximumflux density in the device will occur in a pole when the referencemagnetomotive force F plus the differential magnetomotive force niappears across the air gap with the segment present. If the maximum fluxdensity is the maximum allowable flux density in the iron, is maximumflux in a pole and may be given by the following formula:

max) #0 IBEX d t or rting/ '0 IBEX d t Thus, for any given set of gapdimensions,

F+nim,= =K, (18) and correspondingly,

. 47l'7[.LgtF/Li nx 'max 2 'msx Thus 1" max and g F max= 2( 1 max max vIn order to maximize the factor Fi dFi dmimax) K, (K 1 2m 0 (21) max= l=msx max Using the Equation 23 as a basis for an optimum design,

Thus with the maximum flux density prescribed, optimum output isobtained from the solenoid when the moving segment occupies one-halfofthe air gap length, and the signal and the reference M.M.F.s are equal,that is ni=F. Applying these relationships,

The maximum acceleration or ratio of force to mass for the device isanother important design consideration which can be expressed assumingthat p of density of the iron, in M.K.S. units and the mass is max inalarrmdp then the acceleration is the ratio of, or equal to B force 4mmmass The flux linking the winding 53 is the sum of the fluxes in the twopoles or wherein is the flux to across the gap to pole 45 as (P is theflux across the gap to pole 46.

Thus it is apparent that the total flux linking the coil 53 depends: ontwo variables that is the current and x the length of the gap in whichthe segment is present, then and correspondingly, the induced in thewinding 55, is

The across the windings 53, 55 inseries is This corresponds to a windinginductance of The induced in winding 50 or the reference winding isequal to that of winding 53, since both are linked by the same flux, andits inductance is given as and is dependent upon segment position.

Strong lateral forces may be exerted on the cylindrical segment when thetransducer is energized due to irregularities in the magnetic circuit.For this reason the segment should be carefully aligned and mounted withconsiderable lateral rigidity to prevent misalignment and rubbing on thepole surfaces. Thus the segment 56 may be connected through the shaft 52to an integral part of the device of which it is to operate or may bemounted to lead springs (not shown) which permit axial but not lateralmotion. In operation the single windings 53 and 55 and the referencewinding 50 should be operated or energized from current sources. This isparticularly true on the reference winding since a constantmagnetomotive force or F is desired in the presence of a varying inducedE.M.F. The differential windings may be operated from or controlled fromvacuum tubes, transistors or magnetic amplifiers for continuous controlor from relays, depending upon the desired rate of response. It will berecognized that the device is a high performance electromag netictransducer, in which a force output therefrom is extremely high withrelatively little inertia, and in which the output force is directlyproportional to the driving current, thus differing from theconventional solenoid type apparatus. Finally the signal windings, S3,55 of the linear solenoid actuator have an inductance which is dependentof the position of the movable segment 56. This moving iron linearactuating device provides a relatively simple design which is economicalto manufacture and is simple to maintain and provides high performanceoutput.

I claim:

1. In an electromagnetic transducer, a cylindrical magnetic yoke havingan open and a closed extremity with a centrally located center polemember extending from said closed extremity of said yoke to said openextremity thereof, first and second pole projections integral with saidyoke near said open extremity thereof and concentric with said centerpole member being spaced apart to define with said pole member anannular air gap, a first and second winding positioned in said yokeconcentric with said pole member, a third winding positioned betweensaid first and second pole projections, and a cylindrical armaturemember positioned in said air gap and adapted to move axially relativeto said poles.

2. In an electromagnetic transducer, a cylindrical magnetic yoke havingan open and a closed extremity with a centrally located center polemember extending from said closed extremity of said yoke to said openextremity thereof, vfirst and second pole projections integral with saidyoke near said open extremity thereof and concentric with said centerpole member being spaced apart to define with said pole member anannular air gap, a first and second winding positioned in said yokeconcentric with said pole member, a third winding positioned betweensaid first and second pole projections, and a cylindrical armaturemember having a length equal to the distance between the center lines ofsaid pole projections being positioned in said air gap and adjacent tosaid pole projections and adapted to move axially relative thereto.

3. In an electromagnetic transducer, a cylindrical magnetic yoke havingan open and a closed extremity with a centrally located center polemember extending from said closed extremity of said yoke to said openextremity thereof, first and second pole projections integral with saidyoke near said open extremity thereof and concentric with said centerpole member being spaced apart to define with said pole member anannular air gap, a first and second winding positioned in said yokeconcentric with said pole member, a third winding positioned betweensaid first and second pole projections, and an annular shaped memberpositioned in said air gap and adjacent to said pole projections andadapted to move axially relative thereto.

4. In an electromagnetic transducer, a cylindrical magnetic yoke havingan open and a closed extremity with a centrally located center polemember extending from said closed extremity of said yoke to said openextremity thereof, first and second pole projections integral with saidyoke near said open extremity thereof and concentric with said centerpole member being spaced apart to de fine with said pole member anannular air gap, a first and second winding positioned in said yokeconcentric with said pole member, a third winding positioned betweensaid first and second pole projections, said first winding adapted to beenergized from a constant current source and said second and thirdwindings adapted to be simultaneously energized from a variable source,and armature means positioned in said air gap and adapted to moveaxially relative to said pole members.

5. In an electromagnetic transducer, a cylindrical magnetic yoke havingan open and a closed extremity with a centrally located center polemember extending from said closed extremity of said yoke to said openextremity thereof, first and second pole projections integral with saidyoke near said open extremity thereof and concentric with said centerpole member being spaced apart to define with said pole member :anannular air gap, a first and second winding positioned in said yokeconcentric with said pole member, a third winding positioned betweensaid first and second pole projections, means adapted to connect saidfirst winding to an energizing source, further circuit means connectingsaid second and third windings in a serial relation and to a variablesource, and a cylindrical armature member positioned in said gap andadapted to move axially relative to said pole member and saidprojection.

6. In an electromagnetic transducer, a cylindrical mag netic yoke closedat one extremity and having a centrally located magnetic pole memberextending from the closed extremity toward the opposite extremity, apair or magnetic poles integral with said yoke and positioned near saidopposite extremity being spaced at different distances from said closedextremity, first and second winding means electromagnetioally linkingboth of said spaced poles through said centrally located pole member, athird winding means eleotromagnetically linking only one of said spacedpoles on said yoke located the furthest distance from said closedextremity, means energizing said first winding means to provide areference magnetomotive force between said poles and said centrallylocated pole member, means energizing said second and third windingmeans simultaneously and variably, and a segment of magnetic materialpositioned between said poles and said centrally located pole member andadapted to be motivated by said magnetomotive force supplied by all ofsaid winding means.

7. In an electromagnetic transducer, acylindrical magnetic yoke closedat one extremity and having a centrally located magnetic pole memberextending from the closed extremity toward the opposite extremity, apair of magnetic poles integral with said yoke and positioned near saidopposite extremity being spaced at different distances from said closedextremity, first and second Winding means electromagnetically linkingboth of said spaced poles through said centrally located pole member, athird winding means electromagnetically linking only one of said spacedpoles on said yoke located the furthest distance from said closedextremity, means energizing said first winding means to provide areference magnetomotive force between said poles and said centrallylocated pole member, means energizing said second and third windingmeans simultaneously and variably, and an annular shaped magnetic memberpositioned between said poles and said centrally located pole member andadapted to move relative thereto in response to the energization of allof said winding means.

8. In an electromagnetic transducer, a cylindrical magnetic yoke closedat one extremity and having a centrally located magnetic pole memberextending firom the closed extremity toward the opposite extremity, apair of magnetic poles integral with said yoke and positioned near saidopposite extremity being spaced at diflerent distances from said closedextremity, first and second means electromagneti-cally linking both ofsaid spaced poles through said centrally located pole member, a thirdwinding means electromagnetically linking only one of said spaced poleson said yoke located the furthest distance from said closed extremity,means energizing said first winding means to provide a referencemagnetomotive' force between said poles and said centrally located polemember, means energizing said second and third winding meanssimultaneously and variably, and an annular shaped magnetic memberpositioned between said poles and said centrally located pole member andadapted to move relative thereto in response to the energization of allof said' winding means, said annular shaped member having a length equalto the distance between centers of said pair of spaced magnetic poles.

References Cited in the file of this patent UNITED STATES PATENTS1,931,701 Pvasooe Oct. 24, 1933

